If you attempt to complete a vaccine and do not include a lot # and expiration date, initially you will see a warning message at the bottom of the form stating "Lot # and expiration date are required to generate a valid vaccine certificate. Click save to continue." You can still submit the form if you click "save" one more time. Lot # and expiration date aren't required fields. The message just functions as a warning that you won't have complete vaccine details or a legally valid rabies certificate without these fields.